This invention relates to an improved method and apparatus for gaseous fuel combustion, useful in many applications. This invention also relates to the production of furnace-type carbon black, utilizing a hot stream of gases produced by the burner apparatus of the invention, and injecting into the hot gases a suitable feedstock hydrocarbon under proper flow conditions. More particularly, the invention relates to an improved method and apparatus for producing carbon black whereby heat is generated in an especially advantageous manner and in which the conditions of flow of the hot gases and the manner of introduction of the hydrocarbon feedstock are such as to allow a highly desirable versatility in the production of a wide range of particle size and structure of furnace carbon blacks demanded by the market.
Carbon blacks are produced by several processes, the most common being the channel process, the thermal process and the furnace process. This historic channel process produces carbon black by the impingement of flames of gaseous fuel on channel irons in an environment of air deficiency. Because of the price and supply of natural gas, the process is much less used than formerly. The thermal process is a cyclic process which contacts hydrocarbon gases cyclically with hot checkerwork, and produces a coarse carbon black of low structure. The thermal blacks are used largely as fillers where a minimum of reinforcement of rubber is required. The furnace process is more economical than these two. In the furnace process, a hydrocarbon fuel is burned in a closed vessel, usually refractory-lined, to produce hot combustion product gases and another hydrocarbon stream is injected into the hot gases of combustion to be carbonized and form the product. The secod hydrocarbon stream from which the carbon black is made is commonly referred to as the "make" or "feedstock" stream.
In the furnace processes, the feedstock may be a gas, but for both economic and quality reasons, an aromatic hydrocarbon oil is the material of choice. The fuel may be a gas or an oil, but where gas is available and is economical, it is the fuel of choice.
Oil furnace carbon black reactors are generally of circular cross section and elongate configuration, and are functionally composed of several zones. The first zone is the zone of combustion in which fuel and air are burned to produce hot combustion product gases which supply heat for the process. The heat-supplying combustion process is of critical importance, because the temperature of the combustion products determines to a great degree the quality of the carbon black produced. In addition, a combustion system which results in uneven burning may cause marked and harmful temperature gradients within a reactor, thus subjecting one portion of the feedstock to a different temperature than another portion of the feedstock. Unburnt fragments of a non-aromatic fuel may also interfere with the kinetics of carbonization of the aromatic oil. It is also important that the hot gases leaving the zone of combustion flow in such a manner that the aerodynamic pattern is favorable to the formation of the quality of carbon black desired.
The most efficient burners heretofore known for carbon black reactors utilized vortex or tangential flow of the gases in order to achieve sufficient mixing of the air and fuel gas for complete, uniform combustion. However, a characteristic of such a burner is that the hot combustion products continue to have a vortex, or tangential flow, pattern as they exit from the burner and enter the carbon black reactor proper. This is less desirable for the production of certain types of carbon black than is axial or linear flow of the reaction products. On the other hand, linear flow of the combustion product gases, where desired, has heretofore been achieved only through burners which are less efficient and advantageous than either vortex burners or the burners of the present invention. Therefore, combination of the burner of the present invention, with the other elements of a carbon black reactor, as hereinafter described, provides for highly efficient combustion of the fuel gas and air while at the same time producing linear or axial flow of the combustion products as they are fed to the reaction zone of the carbon black reactor.
The second zone in the reactor is the zone of reaction, in which the oil is dehydrogenated, nucleated as carbon, accreted into chains or clusters to form what is known as structure, and formed into the ultimate particle size it will attain. In the electron microscope, carbon black typically appears as more or less spheroidally shaped particles fused together in clusters or chains. The degree of such clustering or chaining is the degree of structure of the material. When compounded into rubber formulations, blacks with higher structure produce stiffer compounds, and may be compounded with higher proportions of extender oil, which is an economic advantage. In some degree, higher structure contributes to the resistance to abrasion of rubber used in treads of automobile tires. However, for some uses in rubber, lower levels of structure are required. Therefore, it is ncecessary that the manufacturer of carbon black be able to make a range of structure levels to meet the market demands.
The third zone of the carbon black process is the quench zone in which the reactor is rapidly cooled by water injection. After the formation of the carbon, prolonged exposure to high heat damages the properties of the rubber formulations made with the product. The choice of the position of the water stream which quenches the reaction may be properly made by those skilled in the art of carbon black manufacture. If quenched too soon, the process will produce an oily carbon; if quenched too late, the process will produce a black with a damaged surface.